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Future emission legislation can be met through substantial improvement in the effectiveness of the exhaust gas after-treatment system, the engine and the engine management system. For the catalytic converter, differentiation is necessary between the cold start behavior and the effectiveness at operating temperature. To be catalytically effective, a converter must be heated by the exhaust gas up to its light-off temperature. The major influential parameter for the light-off still is the supply of heat from the exhaust gas. Modification of the cold start calibration of engine control such as spark retard or increased idle speed can increase the temperature level of the exhaust gas. One further possibility is represented by a reduction of the critical mass ahead of the catalyst (exhaust manifold and pipe). Nevertheless the best measure to obtain optimal cold start effectiveness still seems to be locating the converter close to the engine.

1 An experimental study has been carried out on a production vehicle by means of roller-bench emission tests in order to optimize alternative aftertreatment systems. To this aim different comparisons between the production exhaust system and new strategies are discussed in the present paper with aid of both modal emission data and bag tailpipe figures. The present work shows the application of a alternative solution that complies with future emission legislation with regard both to HC, CO, NOx and PM without any major engine power output or fuel consumption penalty.

The effects of the internal geometry of catalytic converter channels on flow characteristics; exhaust backpressure and overall conversion efficiency have been investigated by means of both numerical simulations and experimental investigations. The numerical work has been carried out by means of a micro scale numerical tool specifically tailored for flow characteristics within converter channels. The results are discussed with aid of flow distribution patterns within the single cell and backpressure figures along the catalyst channel. The results of the numerical investigation provide information about the most efficient channel shapes. An experimental validation of the simulated results has been carried out with a production 3.6 liter, 6-cylinder engine on a dynamic test bench. Both modal and bag emission data have been measured during the FTP-Cycle.

Nearly all real diesel engines operations are leading to low exhaust temperatures. Standard catalyst technique remains therefore for significant time below light-off. To improve the conversion behavior two approaches were made: placement of tailor-fitted catalysts as close as possible to the engine exhaust port before turbocharger and usage of close coupled catalysts with the so-called hybrid design. Both measures are providing visible progress in reducing diesel engine emissions. Tests were made with modern diesel engines both for passenger cars and heavy-duty vehicles.